Milligram : Milligram provides a minimal setup of styles for a fast and clean starting point. Just it! Only 2kb gzipped! It's not about a UI framework. Specially ...
Foundation : An easy to use, powerful, and flexible framework for building prototypes and production code on any kind of device.
UIkit : A lightweight and modular front-end framework
for developing fast and powerful web interfaces.
RECESS : Developed at Twitter to support our internal styleguide, RECESS is a simple, attractive code quality tool for CSS built on top of LESS.
Incorporate it...
lit : a ridiculously small responsive css framework
Ink is a set of tools for quick development of web interfaces.